When neither CONFIG_PCI nor CONFIG_IBMVIO is set/enabled, iommu.c has a
build error. The fault injection code is not useful in that kernel config,
so make the FAIL_IOMMU option depend on PCI || IBMVIO.

Prevents this build error (warning escalated to error):
../arch/powerpc/kernel/iommu.c:178:30: error: 'fail_iommu_bus_notifier' defined but not used [-Werror=unused-variable]
  178 | static struct notifier_block fail_iommu_bus_notifier = {

Fixes: d6b9a81b2a45 ("powerpc: IOMMU fault injection")
Signed-off-by: Randy Dunlap <redacted>
Reported-by: kernel test robot <redacted>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Anton Blanchard <redacted>
---
I was supposed to update this about one month ago, but then I lost
some email and also took a break for a few weeks, then I remembered,
so here it is.

 arch/powerpc/Kconfig.debug |    1 +
 1 file changed, 1 insertion(+)

--- lnx-512-rc1.orig/arch/powerpc/Kconfig.debug
+++ lnx-512-rc1/arch/powerpc/Kconfig.debug

@@ -353,6 +353,7 @@ config PPC_EARLY_DEBUG_CPM_ADDR
 config FAIL_IOMMU
 	bool "Fault-injection capability for IOMMU"
 	depends on FAULT_INJECTION
+	depends on PCI || IBMVIO
 	help
 	  Provide fault-injection capability for IOMMU. Each device can
 	  be selectively enabled via the fail_iommu property.